Gaging head construction

ABSTRACT

A work piece gaging head functioning in association with an electronic circuit, comprising an electrical switch-type gaging structure embodying features providing adjustable positioning to very substantial tolerances and having an indicator point and stem not only adapted to contact a work piece surface for gaging but also being substantially retractable from such surface to allow for excesses of work piece material in the gaging area. The gaging head embodies circuitry components designed to signal the presence of an undersized or an oversized dimension, and to indicate the &#39;&#39;&#39;&#39;go&#39;&#39;&#39;&#39; dimension which lies within the predetermined high and low limits of the gaging system.

United States Patent Kiewicz et al.

[ 51 June 20, 1972 [54] GAGING HEAD CONSTRUCTION [73] Assignee:Inspection Engineering and Equipment,

Inc., Royal Oak, Mich.

[22] Filed: Jan. 4, 1971 [21] Appl. No.: 103,592

[56] References Cited UNITED STATES PATENTS 3,557,462 1/1971 Kiewicz..33/174 5 '24 I g E g i I Primary Examiner-Leonard Forman AssistantExaminer-Paul G. Foldes Attorney--Benjamin W. Colman [57] ABSTRACT Awork piece gaging head functioning in association with an electroniccircuit, comprising an electrical switch-type gaging structure embodyingfeatures providing adjustable positioning to very substantial tolerancesand having an indicator point and stem not only adapted to contact awork piece surface for gaging but also being substantially retractablefrom such surface to allow for excesses of work piece material in thegaging area. The gaging head embodies circuitry components designed tosignal the presence of an undersized or an oversized dimension, and toindicate the go" dimension which lies within the predetermined high andlow limits of the gaging system.

14 Claims, 12 Drawing Figures 3,570,429 SHEET 2 OF 3 PKTENTEBmzo I972INVENTORS FRANK M. KIEWICZ 8 BY PAUL R.ZINK

ATTORNEY I GAGING HEAD CONSTRUCTION The invention involves an improvedgaging head embodying electrical switch-type components for making andbreaking circuits electrically connected to an indicating or signallingsystem. This application discloses improvements over the inventiondisclosed and claimed in the co-pending application of Frank M. Kiewiczand Alfred Schneider, Ser. No. 771,836 filed Oct. 30, 1968, entitledGaging Device System," issued as U.S. Pat. No. 3,557,462 on Jan. 26, 1971. The improve ments in the gaging head disclosed and claimed in theaboveidentified application include features providing a substantialincrease in the gaging span or tolerance, namely from 0.001 to 0.250inch, and an over-travel feature not provided for in the earlierdisclosed gaging head. These improvements are provided not merely by anelongation of elements, but instead by a reorganization of componentsincluding additional elements having substantial advantages in gagingfunction over the earlier disclosed gaging head. It will be understoodby persons skilled in the art that the improvements disclosed herein donot in any way indicate or suggest the obsolescence of the earlierdisclosed gaging head. The improvements of the instant invention,however, materially extend the utility and applications of an electronicgaging head and the functions to be performed by it.

The components of the new improved gaging head are arranged so thatpredetermined high and low limits of a dimension to be gaged are pre-setin thehead, such limits being adjustable and variable at any time at theoption of the user. Variability of the tolerance setting, from 0.001 upto and including 0.250 inch, is such that changes in tolerance can bemade by merely resetting a lock nut, repositioning the upper or highlimit contact plate by tuming the threaded adjusting ring, and relockingthe nut against the adjusting ring to secure the upper contact plate inits new position. Variability is infinite.

The electrical and electronic circuitry operates at low current so thata minimum destructive effect is occasioned to the switch-type contactingelements and surfaces in the gaging head, thereby maintaining anextremely high degree of accuracy for a very long period of time. Thegaging head and circuitry system herein disclosed use minute quantitiesof current with little or no deterioration of the contact faces andpoints. The use of an appropriate low current, with very little or noappreciable arcing effect, permits a much closer positioning of thecontact surfaces so that very small tolerance spans of 0.00] inch, or insome instances less than that, can be achieved.

It is therefore an object of the invention to provide a gaging head inassociation with an electronic signalling system operating at lowcurrent, wherein the improved gaging head embodies features providing asubstantially increased tolerance span and an overtravel feature of theindicator point. Another object is to provide in a switch-type gaginghead a greatly increased span of high and low tolerance limitsindividually and independently established and adapted to function withthe overtravel feature. Yet another object is the provision of arelatively sensitive and easily adjustable gaging head for sensing thepresence of an unders'ize, an oversize, or a within-tolerance dimensionbeing gaged, within substantially wide limits, and for indicating thepresence of any such dimension by a signalling system, and furtherembodying an overtravel feature for the indicator point.

Various further and more specific objects, features and advantages ofthe invention will appear from the description given below, taken inconnection with the accompanying drawings, illustrating by way ofexample a preferred form of the invention. Reference is here made to thedrawings annexed hereto and forming an integral part of thisspecification, in which FIG. 1 is a perspective view of a gaging devicein which the improved gaging heads are arranged for gaging each of threedifierent dimensions of a work piece.

FIG. 2 is an enlarged longitudinal sectional axial view takensubstantially on the line 22 of FIG. 1, through one of the improvedgaging heads.

FIGS. 3 and 4 are slightly enlarged transverse sectional views takensubstantially on the lines 3-3 and 4-4 of FIG. 2.

- dimension.

FIGS. 7 and 8 are transverse sectional views taken substantially on thelines 77 and 8-8 of FIG. 5. v

FIG. 9 is a transverse sectional view taken substantially on the line9-9 of FIG. 6.

FIG. l0,is a fragmentary somewhatenlarged longitudinal sectional view ofthe switching mechanism'in the area of the adjusting ring when themovable contact plate has been moved into contact with the upper contactplate and is gaging a high limit dimension.

FIG. 11 is a schematic wiring diagram of the electronic signallingsystem to which the improved gaging head is electrically connected.

FIG. 12 is a perspective view of a conductor and signalling circuit plugand receptacle utilized in the disclosed embodiment of the invention.

In the preferred embodiment of the invention described and illustratedherein, the gaging system comprisesthe improved gaging head 10electrically connected to and in the circuitry 12. The gaging head, or aplurality of them as illustrated in FIG. I, is adapted to be secured ina gaging fixture 14 having gage head supporting members 16 and 18 soarranged that the gaging head" indicator point makes contact with asurface S of the work piece W that is disposed for gaging in the fixture14.

The gaging head 10 generally comprises a barrel assembly 20, theadjusting ring assembly 22and the cap assembly 24.

The barrel assembly 20 of the improved gaging head comprises the barrel26 having a proximal body portion 28 externally threaded for engagementwith the adjusting ring assembly and a distal hub section 30 externallythreadedfor adjustable engagement with a split bushing 32 which seats inthe opening 34 of the support member 16 (FIG. 2) and is engaged inlocking position upon the barrel portion 30 by a locking set screw 36.The barrel 26 is provided with an axial longitudinal bore 38 adapted toslidingly receive the indicator stem 40 provided with an indicator point42 at its distal end and a hub portion 44 of reduced diameter at itsproximal end about which a biasing return spring 46 is concentricallydisposed within bore Disposed upon and fixedly secured to the distal endof the barrel body portion 28 is the lower contact plate 48 made of anelectrical insulating material such as a rigid stable glass epoxy or ofan equivalent printed circuit board-type material. The contact plate 48is secured to the barrel portion 28 by a pair of guide posts 50,50 whichhave threaded end portions 52,52 of reduced diameter threadedly engagedin the body portion 28 through openings in the lower contact plate 48until the shoulders of the guide posts are fully seated against thecontact plate (FIGS. 6 and 9). The exposed face of the lower contactplate 48 is provided with a copper contact area 54 that is depositedthereon by conventional printed circuit board practices and procedures.Secured to the lower contact plate in the contact area 54 andelectrically connected thereto is the terminal post 56, its lower end 58being provided with an upper shoulder 60 making electrical connectionwith the contact area 54 and being upset at its distal end to fixedlysecure the terminal post to the lower contact plate 48.

The indicator stem hub portion 44 is provided at its distal end with areduced hub 62 securing the metallic movable contact plate 64 to thedistal end of the indicator stem hub portion 44 (FIG. 6). As shown moreclearly in FIG. 4, the metallic contact plate 64 is provided with a pairof diametrically opposed notches 66,66 which make sliding contact withthe guide posts 50,50, and with a notch 68 which clears and makes nocontact with the terminal post 56. The metallic contact plate 64 isprovided with a contact ball 70 fixedly secured in the plane of thecontact plate, having a diameter greater than the thickness of thecontact plate so as to extend beyond each planar side surface thereof,and so disposed that it is normally adapted to make electrical contactand connection with the copper contact area 54 of the lower contactplate 48 under the bias of the indicator stem return spring 46. Thus, asthe indicator stem retracts in its barrel 26, the movable metalliccontact plate 64 slides upon the guide posts 50,50, the contact ball 70breaking contact with the lower plate contact area 54.

The lock nut 72 is threadedly adjustable upon the barrel body portion 28to perform the tolerance adjusting function with the adjusting ringassembly which will be described more specifically below.

The adjusting ring assembly 22 comprises a substantially cylindricalbody 74 having a counterbore 75 and an internally threaded hub section76 of reduced diameter at one end thereof and an internally threadedportion 78 at the other end thereof, a freely movable upper contactplate 80 normally seated and at rest upon the counterbore seat 81 out ofcontact with the contact plate ball 70, and a stop plate 82 fixedlysecured to the distal ends of the guide posts 50,50 by screws 84. Theupper contact plate 80 and the stop plate 82 are each made of aninsulating material such as the rigid stable glass epoxy or equivalentprinted circuit board-type material utilized for the lower contact plate48. The movable upper contact plate 80 is provided with a copperelectrically conductive contact area 86 deposited thereon byconventional printed circuit board practices and procedures. The coppercontact area 86 is disposed on the side facing the movable metal contactplate 64 and extends from the axial center of the plate 80 toward theouter perimeter of the plate intermediate an opening 88 for a guide post50 and an opening 90 for the terminal post 56, particularly asillustrated in FIG. 3. The copper contact area 86 makes electricalconnection and contact with the contact ball 70 of the movable metalliccontact plate 64 when touched thereby.

The tenninal post 56, one end 58 of which is secured to the lower fixedcontact plate 48, further comprises the upper terminal contact member 92and its lower tubular portion 94 telescopically and slidingly disposedabout and upon the tubular terminal contact element 96 having the lowerend portion 58 at its proximal end. A coiled helical spring 98 isslidingly disposed within the chambers of the tubular elements 94 and 96to bias them apart. The upper terminal contact member 92 B is slidinglydisposed in and through opening 100 of the upper fixed stop plate 82.

As the barrel assembly 20 is threadedly advanced outwardly of theadjusting ring hub portion 76, the fixed lower contact plate 48 moveswith it carrying along the tubular contact element 96, thereby allowingexpansion of the coil spring 98 within the upper terminal contactelement 94 and biasing it upwardly to make electrical contact with thelower contact disc 112 in the cap assembly 24.

The cap assembly 24 comprises a cap body 102 having an externallyknurled annular end portion 104 with an internal thread 106 at thedistal end thereof, a counterbore seat 108, a bore 110, contact discs112 and 114, conductors 116, 118 and 120, a conductor insulator plate122 having openings therethrough to pass the conductors as a cable 126to the exit opening 127 of the cap body 102, a tubular guide member 128fixedly secured to the insulator plate 122 at one end and to the contactdiscs 112 and 1 14 adjacent its opposite end, a tubular member 130telescopically secured to and within the said opposite end of the guidemember 128 and having its distal end open and free to receive a coiledhelical spring 132 concentrically arranged upon a plunger rod 134 whichhas a contact head 136 at its distal end disposed to make electricalcontact with the contact area 86 through grommet 138 of the uppermovable contact plate 80 and a head 140 at its opposite end slidinglydisposed within the tubular guide member 128 beyond the telescopingtubular member 130.

The cap assembly 24 is provided further with an externally threaded locksleeve 142 which is threaded into the portion 106 at the distal end ofthe cap body 102, and upon which the internally threaded portion 78 ofthe adjusting ring body can be threadedly secured up to the distal endface of the cap body annular portion 104.

As shown more particularly in FIGS. 5, 7 and 8, the contact discs 112and 1 14 are mounted upon the tubular member at its shoulder 144 formedas an annular rib, the upper portion 146 of which is fixedly andtelescopically secured within the distal end of the tubular guide member128. The contact discs 112 and 114 are tightly secured together betweenshoulder 144 and the distal end face of the guide member 128. A suitableadhesive is also applied to the interface surfaces of the contact discsto improve their mutual adherence. The proximal end 148 of the tubularportion 146 is closed except for an opening which allows the upper endof the plunger rod 134 to slide therethrough. The head on the plungerrod 134 is disposed outwardly of the upper end 148.

The contact disc 112, as illustrated particularly in FIGS. 5 and 8, isprovided on its exposed side with a copper contact ring area 150 whichis circular in design and makes electrical connection with a temrinalpost 152, connecting the conductor 1 16 to the contact area 150, whichin turn is contacted and makes an electrical connection with the uppertenninal contact member 92, a portion of the terminal post 56. The uppercontact disc 114, more particularly illustrated in FIGS. 5 and 7, isprovided with a circular outer ring contact area 154 disposedsubstantially about the perimeter of the contact disc except in the areaadjacent the terminal post 152. A second terminal post 156 makeselectrical connection with this contact area 154 and is connected to theconductor 120 forming part of the cable 126.

The conductor cable assembly 126 issuing through the opening 127 of thecap body 1 02 comprises the insulated conductors 116, 118 and 120leading from and electrically connected to the terminal post 152, thetenninal tubular guide member 128, and the terminal post 156,respectively, and an outer insulating sheath. These conductors 116, 118and 120 terminate in the plug 160 and are each electrically connected tothe conductor prongs 166, 162 and 164, respectively (FIG. 12). Theseplug prongs are arranged for reception in and connection with thecoupling receptacle 130 having prong receiving contact terminals 170,172 and 174 suitably secured therein.

As more particularly illustrated in FIG. 11, the electronic circuitry 12comprises the power plug 176 for connection with a source of alternatingcurrent line voltage con-ductor having conductors 178, 180 and 182leading therefrom. The conductor 178 connects in series a fuse 184, aplug and jack 186, a manually operated on-off switch 188, a second plugand jack and one end of the primary winding of a step-down transformer192. The conductor 182 is connected to the other end of the primarywinding, completing the primary circuit.

The secondary winding of the transformer 192 has one end connected to aconductor 194 which is in turn connected to the conductor 180 and to theseries circuit including the conductor 196, the plug and jack 198, thecapacitor 200, the

diode 202, and the plug and jack 204 connected to the other end of thesecondary winding of the transformer 192, forming a conventionalhalf-wave rectifying circuit. The tapped winding of the secondaryfurther connects in a series circuit by conductor 206 with the plug andjack 208, the resistor 210, the plug and jack 212, the pilot signal lamp214, and the plug and jack 216, forming the pilot lamp circuit. One endof the transformer secondary winding is connected to the alternatingcurrent source ground by way of conductors 194, 180, 196, the plug andjacks 198 and 218, the terminal receptor I72 and the conductor 220. Thecapacitors 200 and 222 are connected in parallel, one side served by theconductor 196, the other side connected to the emitter of the transistor224.

A series circuit comprising the plug and jack 226, the signal lamp 228and the resistor 230 is connected to the terminal receptor 174 and tothe'base of transistor 224. Another series circuit comprising the plugand jack 232, the signal lamp 234 and the resistor 230 is also connectedto the base of the transistor 224, its other end being connected to theterminal receptor 170. A series circuit comprising the resistors 236 and238 is connected to the collector of the transistor 224 at one end andto one junction'of the capacitors 200 and 222 at the other end. Theemitter of the transistor 224 connects to the second junction of thecapacitor 200 and the diode 202. One terminal of the signal lamp 240 isconnected to the junction of the resistors 236 and 238 and its otherterminal to the emitter of the transistor 224.

The electronic circuitry 12 provides indicating means for signalling thepresence in the work piece W, at any particular dimension D being gagedby the gaging head 10, of an undersize dimension by the signal lamp 234,or of an oversize dimension by the signal lamp 228, or an indication bythe signal lamp 240 that the gaged dimension is within the tolerancelimits established by the positions of the lower contact plate 48 andthe upper contact plate 80 when adjusted by the threaded engagement ofthe adjusting ring body 74 upon the threaded portion 28 of the barrel towhich it is locked bythe lock nut 72.

The operation of the improved gaging head 10 in the gaging system ofthis invention is as follows. A masterwork piece W is first positionedin a suitable manner in the fixture l4 designed to support one or moreof the gaging heads 10in gaging relationship to the work piece. Thebarrel hub portion 30 with the split bushing 32 threaded thereon issecured in the fixture opening 34, to be later locked in position by theset screw 36 when the indicator point 42 is finally established inproper gaging position with respect to the surface S of any dimension Dto be gaged. The dimension D may be any diame-- ter, width, thickness orlength of any portion of the work piece W.

The tolerance limits of the gaging head 10 are first established. Thisis done by means of the adjusting ring body 74 which is adjustablythreaded upon the barrel body portion 28. It will be noted, particularlywith reference to FIGS. 1 and 6, that the movable upper contact plate 80is seated directly upon and against the counterbore seat or shoulder 81of the adjusting ring body. It will be further observed that the plungerrod head 136 under the bias of the coil spring 132 bears directly uponand against the upper contact plate grommet or eyelet 138 and makeselectrical connection therewith.

The movable upper contact plate 80 when seated against the counterboreshoulder 81 is spaced a distance from the lower contact plate 48 whichis secured to and against the proximal end of the barrel portion 28, thespacing between their respective printed copper contact portions 86 and54 being substantially equivalent to the tolerance limits for the go"dimension of the work piece being gaged. The travel of the contact ball70 in the movable metal contact plate 64 from one side of the ball tothe other side where it makes contact first with the lower contact plateand then with the upper contact plate is also a measure of the tolerancelimits for this dimension. Once this tolerance limit is established, thelock nut 72 is threadedly secured upon the barrel portion 28 against thedistal end of the adjusting ring hub portion 76; and the latter thenbeing fixed in position, the tolerance spacing of the movable uppercontact plate 80 also becomes fixed.

For normal gaging operation after the work piece has been placed in thefixture 14 in gaging position, the bias of the plunger rod 134 againstthe movable upper contact plate 80 holds the latter to its counterboreseat 81 in a resilient manner under the bias of the coil spring 132.Thus, if the work piece has a flange that interferes with the extendedposition of the indicator point, or the work piece dimension D beinggaged is substantially oversized, the required travel or retraction ofthe indicator stem 40, the metallic movable plate 64 and the uppermovable contact plate 80 may be such as to move the latter upon theguide posts 50,50 against the bias of the plunger rod 134 up to the stopplat 82.

Once the tolerance limits of the lower contact plate 48 and the uppermovable contact plate have been fixed, and the gaging head barrelassembly 20 firmly fixed in the fixture supporting member, the indicatorpoint 42 is positioned against the master work piece W having a knownspecified dimension to be gaged. The setting of the barrel assembly 20is then established, so that movement of the indicator stem 40 properlypositions the metallic movable contact plate 64 for closing one or theother of the signalling circuits, as will be more fully described below.The improved gaging head 10 is especially adapted for use with a workpiece W requiring substantial retraction of the indicator point in orderto allow for insertion and removal of the work piece W on the fixture14, or for work pieces having substantial variation in the dimension tobe gaged. This retraction feature is particularly provided by theextended plunger rod 134 and its biasing spring 132, the tubular guidemembers 128 and 130 in which the plunger rod slides, and the stop plate82 affixed to the distal ends of the guide posts 50,50. The insulatingstop plate 82 sets the limit of travel for the indicator stem so as toprevent damage to the gaging mechanism.

Thus, should a sheet metal part require gaging, though it have extendedflanges in the area adjacent the dimension to be gaged, the indicatorstem 40 and point 42 can be substantially retracted to allow the flangeportion of the work piece to enter the fixture area, After the workpiece has been properly posi tioned in the fixture, the indicator stemis released to gaging position with respect to the work piece surfaceand dimension to be gaged. This retractable feature of the improvedgaging head materially and substantially expands its scope and utility.

The signalling system of the electronic circuitry 12, served by aconventional source of alternating current through the plug 176, issubstantially the same as that described in the Kiewicz et 21].application No. 771,836 filed Oct. 30, 1968. However, for purposes ofthis disclosure, a simple description of the operation of the circuitryis given, although persons skilled in the art will upon reference to theaforesaid application readily understand and appreciate the operationand function of circuitry 12 of this application. Assuming that all oftheplug and jacks described above and illustrated in FIG. 11 are inelectrical contact and connection, when current is introduced to thecircuit through the connector plug 176 and gaging head plug is connectedwith its complementary receptacle 168 (FIG. 12), the pilot lamp 214 isilluminated by current when the manual switch 188 is closed, visuallyindicating that energy is provided for the dimensional signallinginitiated by the gaging head 10. If the dimension D being gaged isundersize, the signal lamp 234 will be lit; when oversize, the signallamp 228 will light up; and when the dimension is within the tolerancelimits established by the spacing between the lower fixed contact plate48 and the upper movable contact plate 80, the signal lamp 240 willlight up.

Undersize signalling is initiated when the indicator stem 44 brings themovable contact plate 64 into ball contact with the copper contact area54 of the lower fixed contact plate 48. Oversize signalling isaccomplished when the ball 70 of the movable contact plate 64 makeselectrical contact with the copper contact area 86 of the upper contactplate 80.

When the dimension D is undersize, the signalling circuit provides acurrent path through a series circuit from the positive side of thehalf-wave rectifier comprising the capacitor 200, the terminal receptor172, the plug prong 164, conductor 120, the terminal post 156, coppercontact ring 154, the cap body 102, the adjusting ring body 74, thebarrel hub portion 28, the indicator stem hub portion 44, the movablemetallic contact plate 64, contact ball 70, the copper contact area 54,terminal post 56, the copper contact area 150, terminal post 152,conductor 116, the plug prong 166, connector terminal 174, the signallamp 234, resistor 230, the base emitter junction of transistor 224, andto the negative side of the half-wave rectifier which is the junction ofthe capacitor 200 and diode 202. The establishment of this currentcircuit through the lamp 234 causes it to become illuminated and signalthe presence of an undersize dimension. The same current flows throughthe base emitter junction of transistor 224 to bias the transistor andcause collector current to flow from the positive side of the half-waverectifier through resistors 238 and 236 and transistor 224 to thenegative side of the half-wave rectifier. This collector current flowthrough resistor 236 causes a voltage drop across the resistor 236 whichlowers the voltage across the signal lamp 240 to a value below thatrequired to illuminate the lamp. In this manner, the establishment ofcurrent through the signal lamp 234 occasioned by the presence of anundersize dimension causes lamp 240 to be extinguished.

An oversize dimension is signalled by travel of the indicator stem 40upwardly, as illustrated in FIGS. 1 and 6, the circuit to signal lamp228 being as follows. A series circuit is provided from the positiveside of the half-wave rectifier through the terminal receptor 172, theplug prong 164, the conductor 120, contact ring 154, cap body 102,adjusting ring body 74, the barrel body portion 28, the indicator stem40, the movable metallic contact plate 64, contact ball 70, the uppermovable contact area 86, the metal eyelet 138, the plunger rod 134, thetubular members 130 and 128, conductor 118, plug prong 162, thereceptacle terminal 170, the conductor to the signal lamp 228, theresistor 230, the base emitter junction of transistor 224 and to thenegative side of the half-wave rectifier at the junction of the diode202 and the capacitor 200. The establishment of this current circuitthrough the signal lamp 228 causes it to become illuminated and signalthe presence of an oversize dimension. The same current flow through thetransistor base emitter junction biases the transistor 224 and causescollector current to flow from the positive side of the half-waverectifier through resistors 236 and 238 and the transistor 224 to thenegative side of the rectifier. Flow of collector current through theresistor 236 effects a voltage drop there-across sufficient to lower thevalue of the voltage across the signal lamp 240 below that required toilluminate it. In this manner, the establishment of current flow throughthe signal lamp 228 due to the presence of an oversize dimension causesthe signal lamp 240 to be extinguished.

If a circuit to either of signalling lamps 228 or 234 should not beclosed, as when the movable metal contact plate 64 and its contact ball70 are disposed in a position intermediate and spaced from the coppercontact area 54 on the lower contact plate 48 and the copper contactarea 86 on the upper movable contact plate 80, occasioned by thedimension D being within the predetermined pre-set tolerance limits,either of the above-described undersize or oversize current circuits tothe signalling lamps 234 and 228 respectively will then be closed,shutting off current through the base-emitter junction of transistor224. Since the transistor will then be biased off, preventing collectorcurrent flow through the resistor 236, the voltage drop across thisresistor will be very small or non-existent, raising the voltage acrossthe signal lamp 240 to a value sufficient to illuminate the lamp bycurrent flow supplied by the half-wave rectifier. Thus, an absence ofcurrent flow through the lamps 234 and 228 causes the signal lamp 240 tobe illuminated, indicating the presence of a within-tolerance dimension.

The signalling circuit portion beyond the secondary winding of thetransformer 192 is of relatively low current, as for example a2-milliampere current to the signal lamps 228, 234 and 240. The on-offpilot lamp 176 is powered by the tapped secondary winding of thetransformer 192. The on-off pilot lamp 214 when illuminated indicatesthe presence of current passing through the electronic signallingcircuit 12 from the power plug 176 through the step-down transformer 192and the diode 202.

The representation of the fixture 14 is to be understood as being merelyschematic, a fixture normally being designed by persons skilled in theart for use with particular work pieces and the gaging equipmentrequired. The gaging device of this invention is particularly adapted tobe used with flanged metal stamping parts or work pieces havingextensions beyond the surfaces and dimensions to be gaged, whereby theretractable feature of the gaging heads is required.

The insulating contact plates and discs 48, 80, 82, 112, 114 and 122 arepreferably made of a glass epoxy or equivalent printed circuitboard-type material. The remainder of the gaging head elements arepreferably made of suitable steel, alu- 4 minum, copper, or othermetallic materials.

It will be observed from the description given above that the retractionof the indicator stem 40 moves the upper movable plate against theplunger rod 134 for a distance up to the under surface of the stop plate82. This distance can be very substantial, for instance as much as fromone to two or more inches, whereby the indicator point 42 can beretracted out of the way of any flange or extension element of the workpiece W adjacent the area of the dimension to be gaged.

The circular printed contact portion of the contact disc 112 and theprinted copper contact ring 154 of the contact disc 114 permitconnection with the terminal post 56 at any rotated position of the capbody 102 with respect to the adjusting ring body portion 74. Inasmuch asthe lower contact plate 48 is maintained in a fixed position by theguide posts 50,50 threadedly secured to the barrel body portion 28 andthe movable metallic contact plate 64 is guided by such guide posts in aposture such that the ball 70 is always in register (a) with the printedcopper contact area 54 of the lower contact plate 48 and (b) with theprinted copper contact area 86 of the upper movable contact plate 80,also positioned upon the guide posts 50,50, the spacing of these coppercontact areas from each other determines the tolerance limitsestablished by the adjusting ring hub portion 76 upon the threadedbarrel body portion 28.

Although a particular preferred embodiment of the invention has beendisclosed herein for purposes of explanation, further modifications orvariations thereof, after study of this specification, will or maybecome apparent to those skilled in the art to which the inventionpertains. Reference should be had to the appended claims in determiningthe scope of the invention.

We claim:

1. In a gaging head for a fixture-type gaging system designed to gage adimension of a workpiece having an excess of material in the gaging arearequiring substantial retraction of the gaging indicator point, theimprovement combination comprising an elongated adjusting ring,

an elongated barrel adjustably secured to one end of the adjusting ring,

an indicator stem slidably movable in said barrel and having anindicator point at its distal end disposed outboard of said barrel formaking surface contact with said workpiece dimension being gaged,

a cap removably secured to the other end of said adjusting ring,

and an electrical switch contained within said adjusting ring and saidcap comprising a first fixed contact plate secured to the proximal endof said barre] within said adjusting ring, a second contact plateaxially movable in said adjusting ring and spaced apart from said firstcontact plate,

movable switch contact means secured to the proximal end of saidindicator stem, intermediate said first and second contact plates, andspaced from said second contact plate in its at-rest position, means forguiding said second contact plate and said movable switch contact meanssecured to said proximal end of said barrel and extending from saidfirst fixed contact plate at the barrel proximal end into the proximalend region of said elongated adjusting ring,

an extensible post secured to said first contact plate within saidadjusting ring and extending into said cap, stop means secured to thedistal end of said guide means for limiting the axial travel of saidsecond contact plate within said adjusting ring, means extending fromsaid cap through said adjusting ring for biasing said second contactplate toward said movable switch contact means,

and contact discs secured within said cap,

one of said discs adapted to be contacted by said terminal post, wherebysaid movable switch contact means and said second contact platearemovable upon said guide means into the upper reaches of saidadjusting ring to said stop means upon substantial retraction of saidindicator stem.

2. The improved gaging head defined in claim 1, wherein said indicatorpoint is disposed outboard from the distal end of said barrel a distancesubstantially equal to or greater than the maximum travel distance ofsaid second contact plate within said adjusting ring, when said gaginghead is fixture-mounted in dimension gaging attitude.

3. The improved gaging head defined in claim 1, wherein said barrel isthreaded externally, an internally threaded split bushing is secured insaid fixture and adapted to adjustably support and secure said threadedbarrel therein.

4. The improved gaging head defined in claim 1, wherein said elongatedadjusting ring comprises a body having a counterbore and a bore thereinadjacent said elongated barrel,

said fixed first contact plate being fixedly secured to the proximal endof said barrel by said guide means and disposed in said bore,

said second contact plate being movably disposed in said counterbore andhaving an at-rest positionupon the seat of said counterbore,

said biasing means bearing upon said second contact plate substantiallyaxially thereof to bias the same toward its atrest position against saidcounterbore seat.

5. The improved gaging head defined in claim 1, wherein said movableswitch contact means comprises a third contact plate secured to theproximal end of said indicator stem and disposed intermediate and spacedfrom said first and second contact plates.

6. The improved gaging head defined in claim 1, and includmg resilientmeans in said barrel biasing said third contact plate toward said firstcontact plate. 7. The improved gaging head defined in claim 1, whereinsaid cap comprises a chambered body,

a hub portion at one end,

a lock sleeve removably secured in said hub portion and adapted tosecurely engage a complementary portion of said adjusting ring.

8. The improved gaging. head defined in claim 7, and wherein saidcontact discs are secured within a counterbore of said cap hub portionby said lock sleeve at a distance removed from said stop means.

9. The improved gaging head defined in claim 1, wherein each of saidcontact discs, in back-to-back relationship, has

a contactarea on the outwardly directed surface thereof,

said one disc facing outwardly of said cap having its contact area onits outer face adapted to make contact with said terminal post.

10. The improved gaging head defined in claim 1, wherein said terminalpost comprises a lower end portion extending throughsaid first contactplate and having a shoulder adjacent said latter plate and being upsetto secure said latter plate against said shoulder,

an upper terminal contact member adapted to make contactwith the contactarea of one of said contact discs and having a lower tubular endportion,

a tubular contact element secured to said lower end portion andtelescopically and slidingly disposed within said lower tubular endportion of said upper terminal contact member,

and resilient means disposed within said tubular'contact element biasingsaid upper terminal contact member therefrom.

11. The improved gaging head defined in claim 10, and

wherein said upper terminal contact member is slidingly disposed in andthrough an opening in said stop means.

12. The improved gaging head defined in claim 5, wherein said movableswitch contact means further comprises a contact ball secured in saidthird contact plate so that a portion of said ball projects from eachside of said plate.

13. The improved gaging head defined in claim 7, wherein said meansbiasing said second contact plate toward said movable switch contactmeans comprises a tubular guide member affixed to and within said capchambered body,

a second tubular member telescopically and slidingly disposed withinsaid guide member,

said contact discs being secured upon said second tubular member againstthe distal end of said guide member,

a plunger rod slidingly disposed in said second tubular member andhaving its distal end projecting outwardly therefrom and into contactwith said second contact plate,

and resilient means biasing said plunger rod distal end into contactwith said second contact plate.

14. The improved gaging head defined in claim 7, wherein said stop meanscomprises a stop plate secured to the distal ends of said guide meansadjacent said lock sleeve.

1. In a gaging head for a fixture-type gaging system designed to gage adimension of a workpiece having an excess of material in the gaging arearequiring substantial retraction of the gaging indicator point, theimprovement combination comprising an elongated adjusting ring, anelongated barrel adjustably secured to one end of the adjusting ring, anindicator stem slidably movable in said barrel and having an indicatorpoint at its distal end disposed outboard of said barrel for makingsurface contact with said workpiece dimension being gaged, a capremovably secured to the other end of said adjusting ring, and anelectrical switch contained within said adjusting ring and said capcomprising a first fixed contact plate secured to the proximal end ofsaid barrel within said adjusting ring, a second contact plate axiallymovable in said adjusting ring and spaced apart from said first contactplate, movable switch contact means secured to the proximal end of saidindicator stem, intermediate said first and second contact plates, andspaced from said second contact plate in its at-rest position, means forguiding said second contact plate and said movable switch contact meanssecured to said proximal end of said barrel and extending from saidfirst fixed contact plate at the barrel proximal end into the proximalend region of said elongated adjusting ring, an extensible post securedto said first contact plate within said adjusting ring and extendinginto said cap, stop means secured to the distal end of said guide meansfor limiting the axial travel of said second contact plate within saidadjusting ring, means extending from said cap through said adjustingring for biasing said second contact plate toward said movable switchcontact means, and contact discs secured within said cap, one of saiddiscs adapted to be contacted by said terminal post, whereby saidmovable switch contact means and said second contact plate are movableupon said guide means into the upper reaches of said adjusting ring tosaid stop means upon substantial retraction of said indicator stem. 2.The improved gaging head defined in claim 1, wherein said indicatorpoint is disposed outboard from the distal end of said barrel a distancesubstantially equal to or greater than the maximum travel distance ofsaid second contact plate within said adjusting ring, when said gaginghead is fixture-mounted in dimension gaging attitude.
 3. THe improvedgaging head defined in claim 1, wherein said barrel is threadedexternally, an internally threaded split bushing is secured in saidfixture and adapted to adjustably support and secure said threadedbarrel therein.
 4. The improved gaging head defined in claim 1, whereinsaid elongated adjusting ring comprises a body having a counterbore anda bore therein adjacent said elongated barrel, said fixed first contactplate being fixedly secured to the proximal end of said barrel by saidguide means and disposed in said bore, said second contact plate beingmovably disposed in said counterbore and having an at-rest position uponthe seat of said counterbore, said biasing means bearing upon saidsecond contact plate substantially axially thereof to bias the sametoward its at-rest position against said counterbore seat.
 5. Theimproved gaging head defined in claim 1, wherein said movable switchcontact means comprises a third contact plate secured to the proximalend of said indicator stem and disposed intermediate and spaced fromsaid first and second contact plates.
 6. The improved gaging headdefined in claim 1, and including resilient means in said barrel biasingsaid third contact plate toward said first contact plate.
 7. Theimproved gaging head defined in claim 1, wherein said cap comprises achambered body, a hub portion at one end, a lock sleeve removablysecured in said hub portion and adapted to securely engage acomplementary portion of said adjusting ring.
 8. The improved gaginghead defined in claim 7, and wherein said contact discs are securedwithin a counterbore of said cap hub portion by said lock sleeve at adistance removed from said stop means.
 9. The improved gaging headdefined in claim 1, wherein each of said contact discs, in back-to-backrelationship, has a contact area on the outwardly directed surfacethereof, said one disc facing outwardly of said cap having its contactarea on its outer face adapted to make contact with said terminal post.10. The improved gaging head defined in claim 1, wherein said terminalpost comprises a lower end portion extending through said first contactplate and having a shoulder adjacent said latter plate and being upsetto secure said latter plate against said shoulder, an upper terminalcontact member adapted to make contact with the contact area of one ofsaid contact discs and having a lower tubular end portion, a tubularcontact element secured to said lower end portion and telescopically andslidingly disposed within said lower tubular end portion of said upperterminal contact member, and resilient means disposed within saidtubular contact element biasing said upper terminal contact membertherefrom.
 11. The improved gaging head defined in claim 10, and whereinsaid upper terminal contact member is slidingly disposed in and throughan opening in said stop means.
 12. The improved gaging head defined inclaim 5, wherein said movable switch contact means further comprises acontact ball secured in said third contact plate so that a portion ofsaid ball projects from each side of said plate.
 13. The improved gaginghead defined in claim 7, wherein said means biasing said second contactplate toward said movable switch contact means comprises a tubular guidemember affixed to and within said cap chambered body, a second tubularmember telescopically and slidingly disposed within said guide member,said contact discs being secured upon said second tubular member againstthe distal end of said guide member, a plunger rod slidingly disposed insaid second tubular member and having its distal end projectingoutwardly therefrom and into contact with said second contact plate, andresilient means biasing said plunger rod distal end into contact withsaid second contact plate.
 14. The improved gaging head defined in claim7, wherein said stop means comprises a stop plate secured to the distalends of said guide means adjacent said lock sleeve.